updated drupal core to 7.51

modules/user/user.install

@@ -49,6 +49,9 @@ function user_schema() {
         'columns' => array('uid' => 'uid'),
       ),
     ),
+    'indexes' => array(
+      'uid_module' => array('uid', 'module'),
+    ),
   );
 
   $schema['role_permission'] = array(
@@ -910,6 +913,15 @@ function user_update_7018() {
   }
 }
 
+/**
+ * Ensure there is a combined index on {authmap}.uid and {authmap}.module.
+ */
+function user_update_7019() {
+  // Check first in case it was already added manually.
+  if (!db_index_exists('authmap', 'uid_module')) {
+    db_add_index('authmap', 'uid_module', array('uid', 'module'));
+  }
+}
 /**
  * @} End of "addtogroup updates-7.x-extra".
  */